Often, there is a need to identify a person through comparison of the person's face with a recorded image of a face. Such situations regularly arise in police investigations where, for example, the police search for a suspect on the basis of a security camera image.
Difficulty arises when the image used for comparison is of poor quality. The lighting in the store might have been poor. The subject might not have been facing the camera or part of the subject's face might have been hidden by bystanders. The image might have been recorded on a medium such as magnetic tape subject to deterioration.
There are advantages in converting the recorded image to a standard frontal and profile composite image similar to the image composed by a person under the guidance of a police artist. Such an image can easily be the basis for comparison. The image can maintain its fidelity despite noise added in transmission and copying. The image can be updated to allow for the passage of time or for modifications associated with a particular area, such as a beard.
Construction of a composite image is an interactive process. A witness working with a police artist guides manipulation of the appearance and location of features such as ears and eyes until she feels that the composite image resembles her memory of the face. A person working with a separate image of a face instead of with a witness has the advantage of not relying on memory. However, the person working with a separate image, lacking a witness to tell him when to stop, relies on his own criteria in deciding when resemblance of the composite image to the separate image is close enough. With an unlimited number of combinations of features and locations available, the person working with a separate image may find himself trying one combination after another, unable to home in on the combination associated with a composite image most similar to the separate image.